1. Technical Field
The invention relates to a sliding bearing element comprising a backing, especially made of steel, said backing is lined with a bearing material and a soft material, wherein the bearing material is capable of sustaining a bearing load and the soft material is of anti-seizure quality. Within the scope of the present invention the slide bearing can consist Of two half cylinders or the slide bearing is a bush. So that the sliding bearing element is either a half cylinder (half-cylinder type) or the element is a bush (bush-type).
2. Related Art
Such sliding bearing elements are used as oil lubricated crankshaft bearings in internal combustion engines. In this case each bearing comprises two half cylinders clamped together in the big end of the connecting rod—the rod bearing or big end bearing—or the cylinder block and a retaining cap—main bearing.
It has been found that the good load sustaining qualities of the bearing alloy and the excellent bearing qualities of the soft alloy impart the bearing the required properties for constituting a high quality bearing with less friction.
On the one hand the bearing has to be capable of sustaining the bearing load. This is achieved by the bearing alloy bonded to the backing, whereby a supporting framework is formed which includes recesses or depressions. The backing itself is of steel or any other material having the required degree of strength in order to serve as a sufficiently strong support for the bearing.
On the other hand the soft alloy is filled in the spaces between the framework of the bearing alloy constituted by the recesses or depressions. The soft alloy makes sure that the bearing is provided with a sliding surface having a low friction-coefficient.
So, the two essential properties—required degree of strength, low friction sliding surface, which are in general opposite requirements—are realized by a combination of two materials of different characteristics, whereby each material is responsible for one specific property of the bearing.
According to the mentioned state of the art the U.S. Pat. No. 2,971,248 discloses a bearing of the species in question and a method of forming such bearings.
The bearing has a backing strip formed of a material A, which is steel or any other material having the required degree of strength necessary to be used as a bearing support structure. One face of this strip is clad with a bearing material B applied thereto by a suitable method and having one of the essential characteristics i.e. that of high load sustaining power. Depressions C are formed in the material B, preferably grooves spaced from each other and running longitudinally of the strip and therefore axially of the bearing shell.
The grooves are then filled with a material D having a different characteristic from that of portion B i.e. an anti-seizure quality. So, material B has a low friction coefficient.
The opposite sides of these grooves are parallel to each other so that the groove is of the same width throughout its entire depth. In other words the walls of the groove are normal to its surface. Within this document the specific shape of the grooves is considered to be of high importance with respect to the method of producing. According to one method recommended by this patent the coating of the bearing consisting of the different materials B and D is concaved subsequent to the filling of the soft material in the grooves. The concaving procedure changes the diameter of the bearing and thereby may change the ratio of the surface area of material B to the surface area of the material D, when the recesses or depressions taper in an inward direction.
The sliding bearing element disclosed in the U.S. Pat. No. 2,971,248 are provided with a series of parallel longitudinal grooves, which are at least partially open at the front ends of the bearing. So, the outer surface of the bearing at its front sides is formed by the soft material at least in parts.
During engine operation the bearing load will result in an axial movement of the soft alloy B. The less resistant material B is squeezed by the load in axial direction and leaves the bearing at its front ends. Such movement leads to fatigue cracking or swaging of the lining and eventual bearing failure.
Another disadvantage of said bearing is that the recesses or depressions, preferably grooves, are generated by procedures like knurling or the like. This stamp step results in a hardening of the bearing material and thereby a reduction in the anyway worse anti-friction properties of the bearing alloy.
If the grooves are formed by broaching or the like, the producing process will be time-consuming and costly. Moreover it may be difficult to get a satisfactory connection between the bearing alloy and the soft alloy and so to form an integral, reliable sliding surface.
The U.S. Pat. No. 5,000,586 also discloses a multilayer plain bearing with a backing layer having an intermediate layer with grooves formed therein and filled with a bearing or sliding material, wherein a selective distribution of harder material and softer material on selected areas of the bearing is provided as a function of specific bearing operating requirements.
Following this document the recommended design enables basically an improved dimensioning of the sliding layer on the bearing portions more subjected to high loads and shaft misalignments. It should also offer a more uniform distribution of pressures of the bearing portions.
However, the grooves are arranged crosswise the bearing length and so are open at the front ends of the bearing at least at parts. The consequences are laid down above in detail.
A similar sliding bearing element is disclosed in the German laid open publication DE 36 21 577 A1 by the applicant himself. These bearings are characterized in that the groove-shaped recesses in the bearing coating are just disposed in a specific circumferential section, which is subjected to the highest loads during engine operation, whereat this section should be smaller than half of the bearing circumference. The creation of the grooves in this disclosure requires an additional machining operation and a subsequent difficult and expensive operation, if the grooves are to be filled with white metal.